AJP - Endocrinology and Metabolism, Vol 241, Issue 2 121-E128, Copyright © 1981 by American Physiological Society
Metabolism of tritium- and 14C-labeled alanine in rats
S. Golden, M. Chenoweth, A. Dunn, F. Okajima and J. Katz
[3-3H]- and [U-14C]alanine were administered to starved rats by bolus
injection and by continuous infusion. The specific activities of alanine,
glucose, and lactate in blood were followed. The tracer kinetics of alanine
depended on the site of tracer administration and sampling. Tracer was
either administered into the aorta and blood sampled from the vena cava
(A-VC mode) or tracer was administered into the vena cava and arterial
blood sampled (V-A mode) (Katz, J. F. Okajima, and A. Dunn. Biochem J. 194:
513-524, 1981). When tracer was infused in the A-VC mode the plateau
specific activity of alanine was about half that obtained in the V-A mode.
The parameters of alanine turnover were calculated from the specific
activities obtained in the A-VC mode. The calculated apparent replacement
rate averaged 1.9 mg.min-1.kg-1 for [U-14C]- and 3.9 mg.min-1.kg-1 for
[3-3H]alanine, indicating a carbon recycling of about 50%. The apparent
contribution of alanine carbon to that of glucose is 15%. The maximal
activity in plasma water is attained at about 5 min after bolus injection
of [3-3H]alanine and that of [14C]glucose in blood is attained about 10 min
after the injection of [U-14C]alanine. Maximal specific activity of [3H]-
and [14C]lactate is attained within about 1 min after injection. The
apparent mean transit time and alanine mass were calculated from the areas
of washout curves after the continuous infusion was terminated. The mean
transit time for [3H]alanine was 10 min and apparent total body mass of
alanine of the order of 40 mg/kg. The apparent means transit time for
[U-14C]alanine ranged from 33 to 66 min corresponding to a mass of the
order of 100 mg/kg of alanine or 40 mg/kg of alanine carbon.
